The objective of the project is to develop a phase sensitive tomosynthesis technique to facilitate breast cancer detection. The digital breast tomosynthesis, which is currently investigated by many research groups, relies on the small difference in x-ray attenuation between breast tissue and lesions, hence it will be limited in its sensitivity and specificity of breast cancer detection. As x-ray wave pass through breast, x-ray undergoes phase- shifts as well. X-ray phase-shift differences between tissue and lesions are several hundreds to one thousand times larger than their attenuation differences. The proposed prototype system switches the breast tomosynthesis from the attenuation-based imaging with low energy x-rays to the phase sensitive imaging with high energy x-rays. Employing a micro-focus x-ray tube operating at high tube-voltages and innovative phase retrieval and 3D image reconstruction methods, the proposed tomosynthesis technique reconstructs the quantitative slice images of breast electron densities. With this technique the radiation dose to breast is reduced many-fold as compared to current digital breast tomosynthesis. The proposed technique has great potential for enhancing the sensitivity and specificity of breast cancer detection.